1. Field of the Invention
The present invention relates to sizing devices. More particularly, the invention relates to a sizing device, adapted for automatic blow mandril adjustment for plastic blow molding machines. A sizing device accordingly to the invention is provided with at least one blow mandril having a cutting edge and a blow nozzle. Said blow mandril may be adjustably guided and borne by a blow mandril carrier, while being lockable in a selected position by at least one setting means. The blow mandril may be axially biased in relation to the blow mandril carrier toward the blow nozzle to a home position and may be able to be moved in an opposite direction until the bias is overcome and the blow mandril bears against the blow mandril carrier.
Herein the term "sizing device" will be understood to mean that unit of a plastic blow mandril machine, which is provided with at least one blow mandril which is moveable relative to a blow mold in order to introduce the blow mandril into a blow opening therefor and to withdraw the same from a mold after a blowing operation. Such blow mandrils may be matched to the configuration of the blown bodies to be produced and may be connected to the sizing device in an exchangeable manner. The position of the blow mandrils on the sizing device may also be capable of being varied. In order for the blow mandrils to be set in an ideal position, the blow mandrils may be arranged in an adjustable manner in a blow mandril carrier.
For the adjustment of blow mandrils, a reciprocating movement of the sizing device is necessary. In the case of a sizing means, which preferably automatically self-centers itself, as disclosed in the German patent publication 3,623,099 C3, a single downward stroke of the sizing device is all that is required. Using this design, it is possible to automatically to set the horizontal and also the vertical position of the blow mandrils at the ideal position with a single working stroke of the sizing device in which case, each blow mandril is aligned coaxially to a conically widening blow opening of the blow mold and a cut, effective over the entire periphery of the cutting edge, in cooperation with the conical face of the blow opening is ensured. After the blow mandrils have been ideally positioned, the ideal position may be locked by manual actuation of clamping means on the sizing device.
2. Description of the Related Technology
In the case of blow molding machines there is a rule of operation to the effect that on overriding a guard means preventing access to the moving parts of the machine, the hydraulic system powering such moving parts is set at zero pressure to prevent any danger to any person putting his hand or his whole body in the way of such moving parts.
For adjustment, it is necessary for the blow mandrils borne on a blow mandril carrier to be unlocked for axial and radial movement in relation to the blow mandril carrier and then after reaching the ideal position to be re-locked in relation to the blow mandril carrier. Since the adjustment operation requires at least one stroke of the sizing device, the guard means must be closed for the hydraulic system to be able to operate. The setting means serving for locking the ideal position of the blow mandril, and which is normally provided with clamping screws, has for example been operated using wrenches with elongated shanks which extend through the guard or, if there was enough room, the setting means was made accessible via a bridge extending above the sizing device. In any case it is necessary to reach into the danger area of the blow machine for which purpose protective grilles, or the like, must be opened or removed and then later moved back into the intended position. Furthermore, ready access must be provided to the actuating means of the clamping device. This is not always free of problems and may conflict with other design criteria, meaning that the actuation of the clamping device may require a certain degree of skill or the use of special-purpose tools.
Consequently, both for reasons of safety and for speed of operations, there is a requirement of designing a plastic blow molding machine of the type described in which no access to the working or danger area of the machine is necessary for the actuation of the setting means.
Technical development has meant that more productive sizing devices are called for. These so-called multiple sizing devices are fitted with a large number of blow mandrils. Each of the blow mandrils must be individually adjusted. Even if automatic adjustment is employed, by means of which all blow mandrils of the multiple sizing system are to be brought into their ideal working position by a single downward working stroke of the sizing device, the adjustment operations required for multiple sizing are slow and expensive because individual actuation of the setting means of each blow mandril is required. release of the blow mandrils before the adjustment stroke and the re-locking of each blow mandril after the adjustment stroke. The process is even slower and more expensive if the previously mentioned hindrances to working are taken into account.
Since it is possible in modem production technology to ensure the position of blow mandrils within a multiple sizing operation with a high degree of accuracy, there has already been a proposal to set the position of the blow mandrils within a multiple sizing system exactly in accordance with the distance between the blow openings on the associated blow molding tool and to install the blow mandrils at radially fixed distances apart in the multiple sizing system. This leads to difficulties despite the use of materials with exactly the same coefficients of thermal expansion and the use of the same blow molding tool. During operation different temperature settings move occur between the blow molding tool on the one hand and the multiple sizing system on the other hand such that the exact alignment of the blow mandrils and the blow openings cannot be ensured. This may result in increased cutting edge wear. If, with a minimum amount of design modification, the radial adjustment of the blow mandrils may be optimized at any time in accordance with respectively occurring thermal conditions then this source of cutting edge wear may be excluded. However, for this to work it is necessary to abandon the use of blow mandrils with a fixed radial distance.
Preferably, together with its carrier, each blow mandril constitutes a replaceable unit called a "module". In addition, those regions of the sizing device at which such units are attached and are able to be changed in position relative to the blow mandrils are called the "module carriers" of the sizing device.